Glow plugs are typically associated with the cylinder chambers of Diesel engines, and are controlled by an associated electronic control module which is arranged to control in real time the amount of energy transferred to each glow plug, so as to reach and hold a predetermined working temperature. The electronic control module drives the electronic switches, generally MOSFET transistors, by means of pulse-width-modulated (PWM) control signals.
The energy transferred to the glow plugs is the key variable to be controlled, and the glow-plug control systems generally monitor both the voltage across each glow plug and the current flowing through each glow plug.
Controlling the energy transferred to the glow plugs means controlling the power transferred thereto during each period of the PWM driving signals applied to the corresponding electronic switches. The duty-cycle of the PWM driving signals is controlled in a closed-loop, in order to supply the desired energy to each glow plug.
With the presently known control systems the best control performances are achieved through a direct determination of the rms values of the voltage and current waveforms for each period of the PWM driving signals. Such a solution involves remarkable difficulties, in particular due to the high sensitivity to external noise and the complexity of the hardware circuitry and the digital processing needed.
Some known solutions are based on sampling the glow plug voltage and current by means of a so-called high sampling task, with a view to digitally computing the rms values thereof. This solution requires expensive and very fast analogue channel converters, and this adversely affects the digital control throughput and the overall cost of the glow plug control system.
In order to avoid the need for a fast sampling task, it has been proposed to sample the glow plug voltage and current only once per period of the PWM driving signals, for instance at the middle of the “on” phase of said signals. Such a solution indeed solves the issue of the fast sampling, but introduces in turn an important error into the calculation of the rms values of the glow plug voltage and current.
In view of the foregoing, it is at least one object of the present invention to provide an improved method and an improved apparatus for controlling glow plugs in a Diesel engine, allowing to overcome the above-outlined inconveniences of the prior art systems. In addition, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.